1. Field of the Invention
The present invention relates, in general, to an apparatus for heat treatment of impact beams for use in automobiles and, more particularly, to an improvement in such an apparatus to uniformly and effectively heat-treat impact beams having a non-circular cross-section, such as an elliptical cross-section, in addition to impact beams having a circular cross-section.
2. Description of the Prior Art
As well known to those skilled in the art, impact beams are installed in the interior of doors of automobiles so as to reduce damage or deformation of the doors caused by external impact in the case of collision of the automobiles against something else and thereby to protect passengers from such external impact.
In order to allow such impact beams to have desired structural properties, such as desired impact resistance and desired impact absorptive power, without increasing weight of the chassis of automobiles, the impact beams have been typically produced by appropriately processing, such as heat-treating, hollow metal tubular members having a circular cross-section. In recent days, another type of impact beam having a non-circular cross-section, such as an elliptical cross-section capable of improving the structural strength and impact resistance of the impact beam, has been proposed and used.
In order to continuously produce such impact beams through a mass production process while accomplishing desired productivity, a plurality of impact beams, having the same dimension, are unidirectionally and continuously conveyed to a desired position using an appropriate conveying means, such as a chain conveyor. During such a unidirectional and continuous conveying process, the impact beams are continuously heat-treated through an induction heating process. In such an induction heating process, the impact beams pass through the center of an annular induction coil at a constant speed.
Therefore, conventional apparatuses for heat treatment of impact beams are designed to horizontally convey the impact beams while allowing the impact beams to pass through the center of an annular induction coil. Such conventional heat treatment apparatuses somewhat effectively accomplish a desired uniform heat-treating effect in the case of impact beams having a circular cross-section since the circular cross-section of the impact beams agree with the profile of the annular induction coil. However, the conventional heat treatment apparatuses are problematic in that they fail to uniformly heat impact beams having a non-circular cross-section, such as an elliptical cross-section. That is, even when the impact beams, having such a non-circular cross-section, precisely pass through the center of the annular induction coil of an apparatus, the impact beams fail to be uniformly heated by the induction coil due to a difference in distance between the external surface of each impact beam and the annular induction coil. In such a case, the resulting impact beams, having a non-circular cross-section, may be undesirably reduced in structural strength in addition to flexural deformation.